This invention relates to improvements in a slidably movable member having a hard carbon-based film which is low in friction, and more particularly to the slidably movable member having the hard carbon-based film suitable to be used in a condition to be in contact with engine lubricating oil, transmission oil or the like.
Hitherto, formation of hard carbon-based films have been proposed and put into practical use. The hard carbon-based films are formed of carbon-based materials such as amorphous carbon (a-C), a hydrogen-containing amorphous carbon (a-C:H), i-carbon (i-C) and diamond like carbon (DLC). The carbon-based films are usually formed by a plasma enhanced chemical vapor deposition (CVD) process in which hydrocarbon gas is plasma-decomposed to form the carbon-based film, or by an ion beam vapor deposition process using carbon and hydrocarbon ions. The thus formed carbon-based film has a high surface hardness and a high surface smoothness, and a high wear-resistance. Additionally, the carbon-based film is low in friction coefficient owing to solid lubricating characteristics, thereby exhibiting a low friction characteristics. The carbon-based film has a friction coefficient of about 0.1 under the condition of no lubrication, whereas a normal steel having a smooth surface has a friction coefficient ranging from 0.5 to 1.0 under the condition of no lubrication.
The hard carbon-based films have been presently applied to slidably movable members or parts to be used in a condition of no lubrication, for example, cutting tools such as a blade of a drill, processing jigs for the cutting tool, metal dies for plastic working, valve cocks and capstan rollers. Additionally, machine parts (such as those of an internal combustion engine) slidably movable in lubricating oil have been increasingly required to be reduced in mechanical loss from the viewpoints of energy saving and environmental protection. Particularly, such machine parts have been required to be lowered in friction by using the above-discussed hard carbon-based film having the solid lubricating characteristics in case that they are used in a section which is in a severe frictional condition causing a high friction loss.